Field of the Invention
The present invention relates generally to a control method, and more particularly to a control method for an image pickup apparatus configured to correct a focus detecting error caused by an aberration of an optical system.
Description of the Related Art
The contrast autofocus (AF) method and the phase difference AF method are known AF methods for an image pickup apparatus. The contrast AF method and the phase difference AF method are widely accepted AF methods for a video camera and a digital still camera, and some image sensors serve as a focus detecting sensor.
Since these AF methods detect a focus state using an optical image, the aberration of an optical system configured to form the optical image may give an error to the focus detection result. Accordingly, a method for reducing this error has been proposed.
Japanese Patent No. 4,504,031 discloses a method for specifying a type of light source based on a distribution characteristic of a light quantity of an object, and for correcting a focus detecting error caused by a chromatic aberration, using previously stored correction data of the specified light source.
Japanese Patent Laid-Open No. 2003-241064 discloses a method for detecting a dominant wavelength based on a wavelength distribution of an object, and for correcting a focus detecting error caused by a chromatic aberration using previously stored correction data corresponding to the dominant wavelength for each wavelength.
The conventional method cannot provide a quick correction corresponding to a characteristic of the object, and has insufficient accuracy.
Japanese Patent No. 4,504,031 needs to store the correction data for each predicted light source, requires a heavy calculation load for specifying the light source, and has only a limited correction effect to a specific light source.
Japanese Patent Laid-Open No. 2003-241064 converts the correction data into a function for each wavelength, reduces a storage capacity, and provides a correction corresponding to the object. However, this method provides the correction corresponding to the dominant wavelength of the light source, and thus cannot provide a correction using a wavelength distribution according to the image capturing characteristic and the focus detection characteristic or provide a sufficient correction precision.
One common problem is that the correction is unnecessary when a focus detecting error caused by the chromatic aberration is small, and this correction causes a calculation load. Since a lens interchangeable type correction system has a different aberrational state for each optical system, individual unit, and type of a camera, a storage of a huge amount of correction data is necessary so as to handle a correction of every combination.